The present invention relates to techniques for varying characteristics of voices.
Heretofore, various techniques have been proposed for converting a voice input by a user (hereinafter referred to as “input voice”) to a voice of different characteristics from the input voice (hereinafter referred to as “output voice”). Japanese Patent Application Laid-open Publication No. 2000-3200, for example, discloses a technique for generating an output voice by adding so-called “breathiness” to an input voice. According to the disclosed technique, an output voice is generating by adding, to an input voice, components of a particular frequency band (corresponding to a third formant of the input voice) of a white noise having uniform spectral intensity over a wide frequency band width.
However, because characteristics of a voice based on an aspirate of a human (hereinafter referred to as “aspirate sound”) are fundamentally different from those of a white noise, it is difficult to generate an auditorily-natural output voice by jut adding a white noise, as a component of an aspirate sound, to an input voice. Similar problem could arise in generation of other voices of various other characteristics than the output voice having breathiness added thereto, such as a voice generated by irregular vibration of the vocal band (hereinafter referred to as “hoarse voice”) and a whispering voice with no vibration of the vocal band. It is generally possible to generate a hoarse voice, by using the known SMS (Spectral Modeling Synthesis) technique to extract harmonic components and non-harmonic components (also called a residual components or noise components) from an input voice, then relatively increasing the intensity of the non-harmonic components and then adding the intensity-increased non-harmonic components to the harmonic components. However, because a hoarse voice of a person involves irregular vibration of the vocal band and is fundamentally different from a voice merely rich in noise components, there would be encountered significant limitations in generating a natural hoarse voice using the conventionally-known technique.